Brakes Questions

hollyshaw, Aug 28, 7:37am
Hello, I'm trying to do my homework and I can't seem to find the answers to a couple of questions. So if anyone can answer a couple of questions for me that would be great!:)

1. A brake booster on a particular car does not hold vacuum while a engine is shut off. List the possible faults other than hoses that could cause this.

2. A brake master cylinder is not holding pressure. The pedal moves slowly to the floor. No fluid is reported and no leaks are evident
- what is the name given to this problem !
- what is the cause of this problem!

Thanks for any help :)
andrewph, Aug 28, 7:54am
1. Diaphram leaking, oneway valve in vac hose/boosterhousing not holding vacumn. 2. problem name bypasssing. Cause worn seals in the mastercylinder causing the brake fliud to bypass the seals. The seals are cup shaped with the inside facing forward and are pushed by the pedal expanding against the brake fluid appling circumfrul force against the bore. As they wear the edge of the seal rounds bypassing.hope that makes sense to you. :)
hollyshaw, Aug 28, 8:17am
thank you very much :)
unbeatabull, Aug 28, 8:26am
I had two very similar questions in my test paper for brakes, 8184 I think the unit was. #2 the name of the problem they wanted was 'by-passing', I got tripped up on that question in the test as I explained it was the fluid leaking pass the seals, but they wanted the term 'by-passing' for the name of the problem :)
unclejake, Aug 28, 8:39am
I am pretty impressed that you can all spell brakes TBH.

Oh my, how my standards have slippered :-)
sr2, Aug 28, 12:34pm
Question one should not be a hole in the diaphragm (the booster is vacuum suspended). It will most likely be a faulty check valve otherwise a pre loaded input shaft (incorrect pedal adjustment) or a leaking input or output seal. Agree with you on number two.
sr2, Aug 28, 1:04pm
LOL, sad but true.
andrewph, Oct 4, 9:45pm
Yes youre right it can be pedal adjustment Sr2 Its been a while since i did the theory.